Systems for differentiating left and right eye images

ABSTRACT

Methods and systems for determining whether an image is of a left eye or a right eye may be used to enhance laser eye surgery systems and techniques. Methods generally involve locating an iris center and/or pupil center on an image of the eye, locating a corneal vertex and/or at least one reflection on the image, and determining whether the image is of a left eye or a right eye, based on the location of the corneal vertex and/or reflection(s) relative to the iris center and/or pupil center. Systems include a laser emitting a beam of an ablative light energy and a computer processor having a computer program for determining whether the image is of a left eye or a right eye, based on a location of the corneal vertex and/or reflection(s) relative to the iris center and/or pupil center.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. Ser. No. 10/784,481 filed Feb.19, 2004.

The present application is related to U.S. patent application Ser. Nos.10/300,714 filed Nov. 19, 2002 (now U.S. Pat. No. 7,044,602 issued onMay 16, 2006), and Ser. No. 10/460,060 filed Jun. 11, 2003 (now U.S.Pat. No. 7,083,609 issued on Aug. 1, 2006); the full disclosures ofwhich are incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates generally to laser eye surgery methods andsystems. More specifically, the present invention relates to methods andsystems for differentiating between left and right eye images.

Known laser eye procedures generally employ an ultraviolet or infraredlaser to remove a microscopic layer of stromal tissue from the cornea ofthe eye to alter the refractive characteristics of the eye. The laserremoves a selected shape of the corneal tissue, often to correctrefractive errors of the eye. Ultraviolet laser ablation results inphoto-decomposition of the corneal tissue, but generally does not causesignificant thermal damage to adjacent and underlying tissues of theeye. The irradiated molecules are broken into smaller volatile fragmentsphotochemically, directly breaking the intermolecular bonds.

Laser ablation procedures can remove the targeted stroma of the corneato change the cornea's contour for varying purposes, such as forcorrecting myopia, hyperopia, astigmatism, and the like. Control overthe distribution of ablation energy across the cornea may be provided bya variety of systems and methods, including the use of ablatable masks,fixed and moveable apertures, controlled scanning systems, eye movementtracking mechanisms, and the like. In known systems, the laser beamoften comprises a series of discrete pulses of laser light energy, withthe total shape and amount of tissue removed being determined by theshape, size, location, and/or number of a pattern of laser energy pulsesimpinging on the cornea. A variety of algorithms may be used tocalculate the pattern of laser pulses used to reshape the cornea so asto correct a refractive error of the eye. Known systems make use of avariety of forms of lasers and/or laser energy to effect the correction,including infrared lasers, ultraviolet lasers, femtosecond lasers,wavelength multiplied solid-state lasers, and the like. Alternativevision correction techniques make use of radial incisions in the cornea,intraocular lenses, removable corneal support structures, thermalshaping, and the like.

Known corneal correction treatment methods have generally beensuccessful in correcting standard vision errors, such as myopia,hyperopia, astigmatism, and the like. By customizing an ablation patternbased on wavefront measurements, it may be possible to correct minoraberrations to reliably and repeatedly provide visual acuity greaterthan 20/20. Methods and systems for providing wavefront measurementscontinue to benefit from improvements and advancements, such as thosedescribed in U.S. patent application Ser. Nos. 10/300,714 and 10/460,060(incorporated above by reference). Of course, wavefront measurementsystems alone cannot eliminate all potential error from a laser eyesurgery procedure. Errors may occur, for example, in transferringinformation from the measurement system to the ablation system or in theoperation of the ablation system. One possible error that may be made isthat a wavefront measurement image of a left eye may be confused with awavefront image of a right eye. This may occur due to a mislabeling ofthe images, misinterpretation of the images by an operator of theablation system, or the like. In a worst case scenario, wavefrontmeasurement data for left and right eyes may accidentally be reversed,so that the treatment for the left eye is performed on the right eye andvice versa.

Therefore, it would be desirable to provide methods and systems fordifferentiating between left and right eye images. Ideally, such methodsand systems would differentiate left and right eye images acquired usingwavefront imaging technology and would reduce the likelihood of humanerror in a laser eye surgery procedure.

BRIEF SUMMARY OF THE INVENTION

In one aspect of the present invention, a method of determining whetheran image of an eye is of a left eye or a right eye involves locating aniris center on the image, locating a corneal vertex on the image, anddetermining whether the image is of a left eye or a right eye, based onthe location of the corneal vertex relative to the iris center. Someembodiments further include locating a center of the pupil of the eye onthe image before locating the center of the iris. In some embodiments,locating the corneal vertex involves locating at least one reflection onthe image, the reflection having been caused by illuminating the eyewhile acquiring the image. In some embodiments, determining whether theimage is of a left eye or a right eye may involve assuming that the atleast one reflection is displaced, relative to the iris center, towardthe nose of the patient from whom the image was acquired. In suchembodiments, the determination step may further include measuring adisplacement of the at least one reflection toward the nose, relative tothe iris center and determining whether the image is of the left eye orthe right eye, based on the measured displacement. Alternatively, thedetermining step may include: measuring a displacement of the at leastone reflection toward the nose, relative to the iris center; comparingthe measured displacement with a predetermined threshold displacement;and determining whether the image is of the left eye or the right eyeonly if the measured displacement is equal to or greater than thepredetermined threshold.

Optionally, the method may further include illuminating the eye andobtaining the image of the eye before the locating steps. In someembodiments, the eye is illuminated with at least one infrared lightsource. For example, the pupil of the eye may be illuminated with atleast two infrared light emitting diodes disposed near an openingthrough which the image is acquired. In some embodiments, the eye imageis obtained using a wavefront imaging device. Again, in some suchembodiments an image of the pupil of the eye may be obtained, andilluminating the eye may optionally involve illuminating the pupil usingat least one infrared light source disposed near an opening throughwhich the eye image is acquired. In some embodiments, the method mayfurther involve performing a customized laser eye surgery procedure onthe eye, based on the determination of whether the image is of a lefteye or a right eye.

In another aspect of the present invention, a method of determiningwhether an image of an eye is of a left eye or a right eye involveslocating a pupil center on the image, locating a corneal vertex on theimage, and determining whether the image is of a left eye or a righteye, based on the location of the corneal vertex relative to the pupilcenter. Again, in some embodiments locating the corneal vertex involveslocating at least one reflection on the image, with the at least onereflection being caused by illuminating the eye while acquiring theimage. Any of the features described above may suitably apply to variousembodiments of this aspect of the invention.

In yet another aspect of the invention, a method of determining whetheran image of an eye is of a left eye or a right eye comprises locating aniris center on the image, locating at least one reflection on the image,and determining whether the image is of a left eye or a right eye, basedon the location of the at least one reflection relative to the iriscenter. As with the embodiments discussed above, the reflection(s) arecaused by illuminating the eye while acquiring the image. Again, thismethod may include any of the features described above.

In another aspect of the invention, a method of performing laser eyesurgery comprises: acquiring a wavefront measurement of an eye;obtaining an image of the eye during the wavefront measurement;generating a treatment for the eye based on the wavefront measurement;determining whether the image is of a left eye or a right eye, based onnasally-directed displacement of a corneal vertex on the image relativeto an iris center on the image; and verifying that a correct eye hasbeen selected on which to perform a laser eye surgery procedure, basedon the determination of whether the image is of a left eye or a righteye. In some embodiments, the step of determining whether the image ofthe eye is of a left eye or a right eye involves: locating the iriscenter on the image; locating the corneal vertex on the image; andcomparing the location of the corneal vertex to the location of the iriscenter.

As mentioned above, in some embodiments the pupil of the eye may firstbe located before locating the iris center. Also in some embodiments,locating the corneal vertex may involve locating at least one reflectionon the image, wherein the at least one reflection is caused byilluminating the eye while acquiring the image. In some embodiments,determining whether the image is of a left eye or a right eye mayinvolve assuming that the at least one reflection is displaced, relativeto the iris center, toward a nose of a patient from whom the image wasacquired. The determination step may optionally include measuring adisplacement of the at least one reflection toward the nose, relative tothe iris center and determining whether the image is of the left eye orthe right eye, based on the measured displacement. Alternatively, thedetermination step may involve: measuring a displacement of the at leastone reflection toward the nose, relative to the iris center; comparingthe measured displacement with a predetermined threshold displacement;and determining whether the image is of the left eye or the right eyeonly if the measured displacement is equal to or greater than thepredetermined threshold.

Various embodiments involve illuminating the eye with one or moreillumination devices such as infrared lights, as described above. Insome embodiments the pupil is illuminated with two infrared lights thatform the reflections on the image as just described.

In another aspect of the invention, a laser eye surgery system includesa laser emitting a beam of an ablative light energy and a computerprocessor configured to receive an image of an eye and at least one of awavefront measurement and an ablation pattern for the eye, the computerprocessor having a computer program for determining whether the image isof a left eye or a right eye, based on a location of corneal vertex onthe image relative to an iris center on the image. The computerprocessor is configured to verify that a correct eye has been selectedon which to perform a laser eye surgery procedure, based on thedetermination and on the wavefront measurement and/or ablation pattern.In some embodiments, the image of the eye comprises a pupil image takenduring the wavefront measurement.

Optionally, the computer processor may be further configured to locatethe iris center and the corneal vertex on the image. For example, thecomputer processor may determine the location of the corneal vertexbased on a location of at least one reflection on the image, with the atleast one reflection being caused by illuminating the eye whileacquiring the image. In some embodiments, the computer processordetermines whether the image is of the left eye or the right eye byassuming that the reflection is located closer than the iris center to anose of a patient from whom the image was obtained. In some embodiments,the computer processor is further configured to measure a distancebetween the iris center and the at least one reflection. Optionally, thecomputer processor may be further configured to compare the measureddistance to a predetermined threshold distance and decide whether aleft-eye/right-eye determination can be made, based on the comparison.

In some embodiments, the system further includes at least one imageacquisition device for obtaining the image. For example, the imageacquisition device may comprise a wavefront imaging device for imaging apupil of the eye. In some embodiments, the wavefront imaging deviceincludes at least one infrared light source disposed near an openingthrough which the pupil image is acquired.

In another aspect of the present invention, a laser eye surgery systemincludes: a laser emitting a beam of an ablative light energy; a lightsource directing light toward a corneal tissue of the eye; a microscopecapturing an image of the illuminated corneal tissue; and a computerprocessor configured to direct a customized pattern of the ablativelight energy toward the eye, the processor having a left/right eyeidentification module generating either a left eye signal or a right eyesignal in response to the corneal tissue image. In some embodiments, themodule generates an indeterminate eye signal when the corneal tissueimage provides insufficient information for generating a left eye signalor a right eye signal. For example, the insufficient information maycomprise an amount of displacement of a corneal vertex location of theeye relative to an iris center of the eye, the amount of displacementbeing less than a predetermined threshold amount. In some embodiments,the processor verifies that a correct eye has been selected on which toperform a laser eye surgery procedure, based on the left eye or righteye signal and on at least one of a wavefront measurement and anablation pattern for the eye.

Further aspects and embodiments of the invention are described ingreater detail below, with reference to the attached drawing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates a simplified laser eye surgery systemaccording to one embodiment of the present invention;

FIG. 2 is a perspective/schematic view of a laser surgery systemaccording to one embodiment of the present invention;

FIG. 3 is a diagram of a wavefront measurement device according to oneembodiment of the present invention;

FIG. 3A is a diagram of an alternative wavefront measurement deviceaccording to another embodiment of the present invention; and

FIG. 4 schematically illustrates a method for distinguishing betweenright eye images and left eye images according to an embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is particularly useful for enhancing the safetyand accuracy of laser eye surgical procedures such as photorefractivekeratectomy (PRK), phototherapeutic keratectomy (PTK), laser in situkeratomileusis (LASIK), and the like. Safety and accuracy is enhanced bydistinguishing right eye images from left eye images, to help ensurethat an eye treatment plan is matched with a proper eye. While thesystem and methods of the present invention are described primarily inthe context of improving laser eye surgery methods and systems, variousembodiments may also be adapted for use in alternative eye treatmentprocedures and systems such as femtosecond lasers and laser treatment,infrared lasers and laser treatments, radial keratotomy (RK), scleralbands, follow up diagnostic procedures, and the like.

Referring to FIG. 1, one embodiment of a system for performing laser eyesurgery includes a laser system 15 coupled to a wavefront measurementdevice 10 that measures aberrations and other optical characteristics ofan entire optical tissue system. The data from such a wavefrontmeasurement device may be used to generate an optical surface from anarray of optical gradients. The optical surface need not precisely matchan actual tissue surface, as the gradients will show the effects ofaberrations which are actually located throughout the ocular tissuesystem. Nonetheless, corrections imposed on an optical tissue surface soas to correct the aberrations derived from the gradients should correctthe optical tissue system. As used herein terms such as “an opticaltissue surface” may encompass a theoretical tissue surface (derived, forexample, from wavefront sensor data), an actual tissue surface, and/or atissue surface formed for purposes of treatment (for example, byincising corneal tissues so as to allow a flap of the cornealepithelium, Bowman's membrane and stroma to be displaced and expose theunderlying stroma during a LASIK procedure).

Referring now to FIGS. 1 and 2, one embodiment of laser eye surgerysystem 15 includes a laser 12 that produces a laser beam 14. Laser 12 isoptically coupled to laser delivery optics 16, which direct laser beam14 to an eye E of a patient. A delivery optics support structure (notshown here for clarity) extends from a frame 18 supporting laser 12. Amicroscope 20 is mounted on the delivery optics support structure, themicroscope often being used to image a cornea of eye E.

Laser 12 generally comprises an excimer laser, typically comprising anargon-fluorine laser producing pulses of laser light having a wavelengthof approximately 193 nm. Laser 12 will preferably be designed to providea feedback stabilized fluence at the patient's eye E, delivered viadelivery optics 16. The present invention may also be useful withalternative sources of ultraviolet or infrared radiation, particularlythose adapted to controllably ablate the corneal tissue without causingsignificant damage to adjacent and/or underlying tissues of the eye.Such sources include, but are not limited to, solid state lasers andother devices which can generate energy in the ultraviolet wavelengthbetween about 185 and 215 nm and/or those which utilizefrequency-multiplying techniques. Hence, although an excimer laser isthe illustrative source of an ablating beam, other lasers may be used inthe present invention.

Laser 12 and delivery optics 16 will generally direct laser beam 14 tothe eye E under the direction of a computer processor 22. Processor 22will generally selectively adjust laser beam 14 to expose portions ofthe cornea to the pulses of laser energy so as to effect a predeterminedsculpting of the cornea and alter the refractive characteristics of theeye. In many embodiments, both laser 14 and the laser delivery opticalsystem 16 will be under computer control of processor 22 to effect thedesired laser sculpting process so as to deliver the customized ablationprofile, with the processor ideally altering the ablation procedure inresponse to inputs from the optical feedback system. The feedback willpreferably be input into processor 22 from an automated image analysissystem, or may be manually input into the processor by a system operatorusing an input device in response to a visual inspection of analysisimages provided by the optical feedback system. Processor 22 will oftencontinue and/or terminate a sculpting treatment in response to thefeedback, and may optionally also modify the planned sculpting based atleast in part on the feedback.

Laser beam 14 may be adjusted to produce the desired sculpting using avariety of alternative mechanisms. The laser beam 14 may be selectivelylimited using one or more variable apertures. An exemplary variableaperture system having a variable iris and a variable width slit isdescribed in U.S. Pat. No. 5,713,892, the full disclosure of which isincorporated herein by reference. The laser beam may also be tailored byvarying the size and offset of the laser spot from an axis of the eye,as described in U.S. Pat. No. 5,683,379, and as also described inco-pending U.S. patent application Ser. Nos. 08/968,380, filed Nov. 12,1997; and Ser. No. 09/274,999 filed Mar. 22, 1999, the full disclosuresof which are incorporated herein by reference.

Still further alternatives are possible, including scanning of the laserbeam over the surface of the eye and controlling the number of pulsesand/or dwell time at each location, as described, for example, by U.S.Pat. No. 4,665,913 (the full disclosure of which is incorporated hereinby reference) and as demonstrated by other scanning laser systems suchas the LSX laser by LaserSight, LadarVision by Alcon/Autonomous, and the217C by Technolas; using masks in the optical path of laser beam 14which ablate to vary the profile of the beam incident on the cornea, asdescribed in U.S. patent application Ser. No. 08/468,898, filed Jun. 6,1995 (the full disclosure of which is incorporated herein by reference);hybrid profile-scanning systems in which a variable size beam (typicallycontrolled by a variable width slit and/or variable diameter irisdiaphragm) is scanned across the cornea; or the like. The computerprograms and control methodology for these laser pattern tailoringtechniques are well described in the patent literature.

Additional components and subsystems may be included with laser system15. For example, spatial and/or temporal integrators may be included tocontrol the distribution of energy within the laser beam, as describedin U.S. Pat. No. 5,646,791, the disclosure of which is incorporatedherein by reference. An ablation effluent evacuator/filter, and otherancillary components of the laser surgery system which are not necessaryto an understanding of the invention, need not be described in detailfor an understanding of the present invention.

As mentioned above, laser system 15 will generally include a computersystem or programmable processor 22. Processor 22 may comprise (orinterface with) a conventional PC system including the standard userinterface devices such as a keyboard, a display monitor, and the like.Processor 22 will typically include an input device such as a magneticor optical disk drive, a CD drive, an internet connection, or the like.Such input devices will often be used to download a computer executablecode from a computer network or a tangible storage media 29 embodyingsteps or programming instructions for any of the methods of the presentinvention. Tangible storage media 29 includes, but is not limited to aCD-R, a CD-RW, DVD, a floppy disk, an optical disk, a data tape, anon-volatile memory, or the like, and the processor 22 will include thememory boards and other standard components of modern computer systemsfor storing and executing this code.

Wavefront measurement device 10 typically includes a wavefrontmeasurement assembly 11 and an imaging assembly 13. Wavefrontmeasurement assembly 11 can be used to measure and obtain a wavefrontelevation surface of at least one of the patient's eyes, and imagingassembly 13 can obtain still or moving images of the patient's eyeduring the wavefront measurement.

In exemplary embodiments, imaging assembly 13 is a CCD camera that canobtain a still image of the patient's eye. The image(s) obtained byimaging assembly 13 can thereafter be used to register the wavefrontmeasurement and/or a customized ablation pattern (based on the wavefrontmeasurement) with the patient's eye during the laser surgical procedure.Various embodiments and features of imaging assembly 13 are described ingreater detail below.

The wavefront measurement assembly 11 and imaging assembly 13 can becoupled to or integral with a computer system 17 that can generate andstore the wavefront measurements and images of the patient's eye.Thereafter, the patient's wavefront data can be stored on a computerreadable medium, such as a CD-R, CD-RW, DVD-R, floppy disk, opticaldisk, a hard drive, or other computer readable medium. Optionally, insome embodiments, the computer system of the wavefront measurementdevice can generate and save an ablation profile based on the wavefrontdata.

The wavefront data and/or the customized ablation profile can be loadedinto a laser surgical system 15 through reading of the computer readablemedium or through delivery into a memory of surgical system 15 over alocal or wide-area network (LAN or WAN). Laser eye surgery system 15 caninclude a computer controller system 22 that is in communication with animaging assembly 20 and a laser assembly 12. Computer system 22 can havesoftware stored in a memory and hardware that can be used to control thedelivery of the ablative energy to the patient's eye, the tracking ofthe position (translations in the x, y, and z directions and torsionalrotations) of the patient's eye relative to an optical axis of laserbeam 14, and the like. In exemplary embodiments, among other functions,computer system 22 can be programmed to calculate a customized ablationprofile based on the wavefront data, register the image(s) taken withwavefront measurement assembly 11 with the image(s) taken by imagingassembly 20, and measure the torsional offset between the patient's eyein the two images. Additionally, computer system 22 can be programmed tomeasure, in real-time, the movement (x(t), y(t), z(t), and rotationalorientation) of the patient's eye relative to the optical axis of thelaser beam so as to allow the computer system to modify the delivery ofthe customized ablation profile based on the real-time position of thepatient's eye. Such features are described more fully in U.S. patentapplication Ser. No. 10/300,714, which was previously incorporated byreference.

Referring now to FIG. 3, one embodiment of a wavefront measurementdevice 10 of the present invention is schematically illustrated. Theillustrated embodiment is merely an example of one wavefront measurementdevice 10, and any of a number of other conventional or proprietarywavefront measurement devices may be used with various embodiments ofthe present invention.

Generally, wavefront measurement device 10 includes an imaging assembly13 that can image the patient's eye E during the wavefront measurement.Imaging assembly 13 includes an image source 32 which projects a sourceimage through optical tissues 34 of eye E to form an image 44 upon asurface of retina R. The image from retina R is transmitted by theoptical system of the eye (specifically, optical tissues 34) and imagedonto a wavefront sensor 36 by system optics 38.

In some embodiments, imaging assembly 13 further includes a pupil camera19, which may be used to acquire one or more pupil images of the eye E.Pupil images are images of the iris of the eye E, typically acquiredwith infrared (IR) illumination. Such images may be used, for example,to determine the size of the pupil of the eye E, to compare iris andpupil locations, to register iris and pupil locations for treatmentand/or the like. In some embodiments, one or more (preferably two)infrared (IR) light emitting diodes (LEDs) 33 are disposed on oppositessides of an opening through which image source 32 projects its sourceimage. IR LEDs generally provide IR illumination for acquiring the pupilimages. The IR illumination produces distinct reflections on the cornealsurface of the eye E, which are visible on each pupil image acquired.

Pupil camera 13 may be in communication with a computer system 17 todeliver the image(s) of the patient's eye E to a memory in computer 17.In various embodiments, computer system 17 may determine a location ofthe pupil of the eye on the pupil image and use that location todetermine a location of the center of the iris of the eye. Techniquesfor determining an iris center location are described more fully in U.S.patent application Ser. No. 10/300,714, previously incorporated byreference. The computer 17 may further determine the location(s) of oneor more reflections (Perkinje images) on a pupil image, caused by the IRillumination, and use the reflection location(s) to determine a locationof a corneal vertex of the eye E. Techniques for determining a cornealvertex location are described more fully in U.S. patent application Ser.No. 10/460,060, which was also previously incorporated by reference.Next, the computer may compare either the corneal vertex location, thelocation of one or more reflections, or both with the iris centerlocation. It has been found that the location of the reflections and/orthe corneal vertex are typically nasally displaced relative to the iriscenter in an eye. In other words, the computer system 17 may assume thata reflection and/or a corneal vertex on a pupil image is closer to thepatient's nose than the iris center is. By comparing the reflectionand/or corneal vertex location to the iris location, the computer system17 can determine if a given pupil image is of a left eye or a right eye.

The location of the optical axis of the eye E may also be verified byreference to the data provided from pupil camera 19. In the exemplaryembodiment, pupil camera 19 images pupil 50 and/or the iris so as toallow subsequent determination of a position and torsional orientationof the pupil and/or iris for registration of the wavefront sensor datarelative to the optical tissues, as is described more fully in U.S.patent application Ser. No. 10/300,714, previously incorporated byreference.

Wavefront sensor 36 can also communicate signals to computer 17 fordetermination of a corneal ablation treatment program. Computer 17 maybe the same computer which is used to direct operation of the lasersurgery system 15, or at least some or all of the computer components ofthe wavefront measurement device 10 and laser surgery system may beseparate. Data from wavefront sensor 36 may be transmitted to lasersystem computer 22 (FIG. 1) via tangible media 29, via an I/O port, viaan networking connection such as an intranet, the Internet, or the like.

Wavefront sensor 36 generally comprises a lenslet array 38 and an imagesensor 40. As the image from retina R is transmitted through opticaltissues 34 and imaged onto a surface of lenslet array 38, the lensletarray separates the transmitted image into an array of beamlets 42, and(in combination with other optical components of the system) images theseparated beamlets on the surface of sensor 40. Sensor 40 typicallycomprises a charge coupled device (CCD) and senses the characteristicsof these individual beamlets, which can be used to determine thecharacteristics of an associated region of optical tissues 34. Inparticular, where image 44 comprises a point or small spot of light, alocation of the transmitted spot as imaged by a beamlet can directlyindicate a local gradient of the associated region of optical tissue.

Eye E generally defines an anterior orientation ANT and a posteriororientation POS. Image source 32 generally projects an image in aposterior orientation through optical tissues 34 onto retina R. Opticaltissues 34 again transmit image 44 from the retina anteriorly towardwavefront sensor 36. Image 44 actually formed on retina R may bedistorted by any imperfections in the eye's optical system when theimage source is originally transmitted by optical tissues 34. In someembodiments, image source projection optics (not shown) may beconfigured or adapted to decrease any distortion of image 44.

In some embodiments, image source optics may decrease lower orderoptical errors by compensating for spherical and/or cylindrical errorsof optical tissues 34. Higher order optical errors of the opticaltissues may also be compensated through the use of an adaptive opticelement, such as a deformable mirror. Use of an image source 32 selectedto define a point or small spot at image 44 upon retina R may facilitatethe analysis of the data provided by wavefront sensor 36. Distortion ofimage 44 may be limited by transmitting a source image through a centralregion 48 of optical tissues 34 which is smaller than a pupil 50, as thecentral portion of the pupil may be less prone to optical errors thanthe peripheral portion. Regardless of the particular image sourcestructure, it will be generally be beneficial to have well-defined andaccurately formed image 44 on retina R.

While the method of the present invention will generally be describedwith reference to sensing of an image 44 on the retina, it should beunderstood that a series of wavefront sensor data readings may be taken.For example, a time series of wavefront data readings may help toprovide a more accurate overall determination of the ocular tissueaberrations. As the ocular tissues can vary in shape over a brief periodof time, a plurality of temporally separated wavefront sensormeasurements can avoid relying on a single snapshot of the opticalcharacteristics as the basis for a refractive correcting procedure.Still further alternatives are also available, including takingwavefront sensor data of the eye with the eye in differingconfigurations, positions, and/or orientations. For example, a patientwill often help maintain alignment of the eye with wavefront device 10by focusing on a fixation target, as described in U.S. Pat. No.6,004,313, the full disclosure of which is incorporated herein byreference. By varying a focal position of the fixation target asdescribed in that reference, optical characteristics of the eye may bedetermined while the eye accommodate or adapts to image a field of viewat a varying distance. Further alternatives include rotating of the eyeby providing alternative and/or moving fixation targets within wavefrontdevice 10.

An alternative embodiment of a wavefront sensor system is illustrated inFIG. 3A. The major components of the system of FIG. 3A are similar tothose of FIG. 3. Additionally, FIG. 3A includes an adaptive opticalelement 52 in the form of a deformable mirror. The source image isreflected from deformable mirror 52 during transmission to retina R, anddeformable mirror 52 is also along the optical path used to form thetransmitted image between retina R and imaging sensor 40. Deformablemirror 52 can be controllably deformed to limit distortion of the imageformed on the retina, and may enhance the accuracy of the wavefrontdata. The structure and use of the system of FIG. 3A are more fullydescribed in U.S. Pat. No. 6,095,651, the full disclosure of which hisincorporated herein by reference.

The components of one embodiment of a wavefront system for measuring theeye and ablations comprise elements of a VISX WaveScan®, available fromVISX, Incorporated of Santa Clara, Calif. A preferred embodimentincludes a WaveScan with a deformable mirror as described above. Analternate embodiment of a wavefront measuring device is described inU.S. Pat. No. 6,271,915, the full disclosure of which is incorporatedherein by reference.

A treatment program map may be calculated from the wavefront elevationmap so as to remove the regular (spherical and/or cylindrical) andirregular errors of the optical tissues. By combining the treatmentprogram with a laser ablation pulse characteristics of a particularlaser system, a table of ablation pulse locations, sizes, shapes, and/ornumbers can be developed. An exemplary method and system for preparingsuch an ablation table is described in co-pending U.S. patentapplication Ser. No. 09/805,737 filed on Mar. 13, 2001 and entitled“Generating Scanning Spot Locations for Laser Eye Surgery,” the fulldisclosure of which is incorporated herein by reference. Ablation tablemay optionally be optimized by sorting individual pulses to avoidlocalized heating, minimize irregular ablations if the treatment programis interrupted, and the like.

Based on the wavefront measurements of the eye, a corneal ablationpattern may be calculated by computer processor 17 or 22 (or by anotherseparate processor) for ablating the eye with laser ablation system 15to correct the optical errors of the eye. Such calculations will oftenbe based on both the measured optical properties of the eye and on thecharacteristics of the corneal tissue targeted for ablation (such as theablation rate and the refractive index). The results of the calculationwill often comprise an ablation pattern in the form of an ablation tablelisting ablation locations, numbers of pulses, ablation sizes, and orablation shapes to effect the desired refractive correction. Anexemplary method for generating ablation patterns is described inco-pending U.S. patent application Ser. No. 09/805,737, the fulldisclosure of which was previously incorporated herein by reference.Where the refractive error is to be corrected by alternative treatmentmodalities, alternative treatment plans may be prepared, such as acorneal implant or the like.

Referring now to FIG. 4, an exemplary method for determining whether animage is of a left eye or a right eye, as described above, suitablyincludes a first step of acquiring an image of the eye 60. The image,for example, may be a pupil image. A pupil center may then be located onthe pupil image 62. This locating step, as well as many or allsubsequent steps, may be achieved in some embodiments via imageprocessing software or other software. Such software may then be used tolocate an iris center 64 and a corneal vertex 66 on the pupil image. Insome embodiments, locating the corneal vertex 66 may involve firstlocating one or more reflections on the pupil image caused by infraredillumination used to acquire the image. Once the corneal vertex and irislocations have been determined, the displacement of the vertex relativeto the iris may be determined 68. The image processing software or othersuitable software then determines whether the displacement of the vertexrelative to the iris is greater than or equal to a threshold amount ofdisplacement 70. If not, then no determination is made as to whether theimage is of a left or a right eye 72. If the vertex displacement meetsor exceeds the threshold, then a determination is made as to whether theimage is of a left or a right eye 74. As described above, thisdetermination is made based on the fact that the vertex is almost alwaysnasally displaced relative to the iris center.

When a determination is made as to whether an image is of a left eye ora right eye, such determination may be used as a safety check in a lasereye surgery procedure. For example, the determination as to whether theimage is of a left or right eye may be checked against a treatment planfor an eye on which a procedure is about to be performed. If thetreatment plan matches the eye that is represented in the image, thenthe procedure may proceed as planned. If the treatment plan and theimage do not match—for example, if the image is of a right eye and thetreatment plan is for a left eye—then the laser surgery system may betriggered to provide a warning or alarm that the wrong eye is about tobe operated upon. In other embodiments, a mismatch may cause the lasersurgery system to shut down temporarily. Any suitable technique forproviding a safety check may be incorporated in various embodiments.

In other embodiments, various changes may be made to the method justdescribed while still achieving similar results. For example, instead oflocating the iris center, some embodiments may skip that step andcompare the corneal vertex location to the pupil center location. Inother embodiments, the step of locating the corneal vertex may beskipped, and the displacement of one or more reflections on the pupilimage relative to the iris center and/or pupil center may be used tomake the left/right determination. In some embodiments, the left/rightdetermination may be made without first comparing the vertex to athreshold amount. And in yet other embodiments, the order of steps maybe altered. For example, it may be advantageous in some embodiments todetermine a corneal vertex location before an iris center location.Thus, the method described above is but one embodiment and is providedprimarily for exemplary purposes.

While the above provides a complete and accurate description of specificembodiments of the invention, a number of changes and adaptations of thepresent invention may be readily made. Therefore, the scope of theinvention is limited solely by the following claims.

1. A laser eye surgery system comprising: a laser emitting a beam of ablative light energy; and a computer processor configured to receive an image of an eye and at least one of a wavefront measurement and an ablation pattern for the eye, the computer processor having a computer program for determining whether the image is of a left eye or a right eye, based on a location of corneal vertex on the image relative to an iris center on the image, wherein the computer processor is configured to verify that a correct eye has been selected on which to perform a laser eye surgery procedure, based on the determination and on the wavefront measurement and/or ablation pattern.
 2. A system as in claim 1, wherein the image of the eye comprises a pupil image taken during the wavefront measurement.
 3. A system as in claim 1, wherein the computer processor is further configured to locate the iris center and the corneal vertex on the image of the eye.
 4. A system as in claim 3, wherein the computer processor determines the location of the corneal vertex based on a location of at least one reflection on the image, wherein the at least one reflection is caused by illuminating the eye while acquiring the image.
 5. A system as in claim 4, wherein the computer processor determines whether the image is of the left eye or the right eye by assuming that the at least one reflection is located closer than the iris center to a nose of a patient from whom the image was obtained.
 6. A system as in claim 5, wherein the computer processor is further configured to measure a distance between the iris center and the at least one reflection.
 7. A system as in claim 6, wherein the computer processor is further configured to compare the measured distance to a predetermined threshold distance and decide whether a left-eye/right-eye determination can be made, based on the comparison.
 8. A system as in claim 1, further comprising at least one image acquisition device for obtaining the image.
 9. A system as in claim 8, wherein the image acquisition device comprises a wavefront imaging device for imaging a pupil of the eye.
 10. A system as in claim 8, wherein the wavefront imaging device includes at least one infrared light source disposed near an opening through which the pupil image is acquired.
 11. A laser eye surgery system comprising: a laser emitting a beam of an ablative light energy; a light source directing light toward a corneal tissue of the eye; a microscope capturing an image of the illuminated corneal tissue; and a computer processor configured to direct a customized pattern of the ablative light energy toward the eye, the processor having a left/right eye identification module generating either a left eye signal or a right eye signal based on a location of corneal vertex on the corneal tissue image relative to an iris center on the corneal tissue image.
 12. A system as in claim 11, wherein the module generates an indeterminate eye signal when the corneal tissue image provides insufficient information for generating a left eye signal or a right eye signal.
 13. A system as in claim 12, wherein the insufficient information comprises an amount of displacement of the corneal vertex location of the eye relative to the iris center of the eye, the amount of displacement being less than a predetermined threshold amount.
 14. A system as in claim 11, wherein the processor verifies that a correct eye has been selected on which to perform a laser eye surgery procedure, based on the left eye or right eye signal and on at least one of a wavefront measurement and an ablation pattern for the eye. 